Measurement of Aβ Amyloid Plaques and Tau Protein in Postmortem Human Alzheimer’s Disease Brain by Autoradiography Using [18F]Flotaza, [125I]IBETA, [124/125I]IPPI and Immunohistochemistry Analysis Using QuPath

Abstract

High-resolution scans of immunohistochemical (IHC) stains of Alzheimer’s disease (AD) brain slices and radioligand autoradiography both provide information about the distribution of Aβ plaques and Tau, the two common proteinopathies in AD. Accurate assessment of the amount and regional location of Aβ plaques and Tau is essential to understand the progression of AD pathology. Our goal was to develop a quantitative method for the analysis of IHC–autoradiography images. Postmortem anterior cingulate (AC) and corpus callosum (CC) from AD and control (CN) subjects were IHC stained with anti-Aβ for Aβ plaques and autoradiography with [18F]flotaza and [125I]IBETA for Aβ plaques. For Tau, [124I]IPPI, a new radiotracer, was synthesized and evaluated in the AD brain. For Tau imaging, brain slices were IHC stained with anti-Tau and autoradiography using [125I]IPPI and [124I]IPPI. Annotations for Aβ plaques and Tau using QuPath for training and pixel classifiers were generated to measure the percent of the area of Aβ plaques and Tau in each slice. The binding of [124I]IPPI was observed in all AD brains with an AC/CC ratio > 10. Selectivity to Tau was shown by blocking [124I]IPPI with MK-6240. Percent positivity for Aβ plaques was 4–15%, and for Tau, it was 1.3 to 35%. All IHC Aβ plaque-positive subjects showed [18F]flotaza and [125I]IBETA binding with a positive linear correlation (r2 > 0.45). Tau-positive subjects showed [124/125I]IPPI binding with a stronger positive linear correlation (r2 > 0.80). This quantitative IHC–autoradiography approach provides an accurate measurement of Aβ plaques and Tau within and across subjects.

Glutamate’s Effects on the N-Methyl-D-Aspartate (NMDA) Receptor Ion Channel in Alzheimer’s Disease Brain: Challenges for PET Radiotracer Development for Imaging the NMDA Ion Channel

“…Immunostaining of all brain sections was carried out by the pathology services of the University of California-Irvine, using Ventana BenchMark Ultra protocols and analyzed using QuPath, as previously described [34].…”

[125I]INFT: Synthesis and Evaluation of a New Imaging Agent for Tau Protein in Post-Mortem Human Alzheimer’s Disease Brain

“…Off-target binding to MAO-B of these radioiodinated derivatives has not been reported. We have previously reported azaindole derivatives [ 125 I]IPPI [14] and [ 124 I]IPPI [15] as radioiodinated analogs of [ 18 [ 124/125 I]IPPI to Tau was observed in the anterior cingulate of postmortem human AD brains. The binding of [ 124/125 I]IPPI was quantitatively correlated with the Tau load measured by anti-Tau immunohistochemistry of the same subjects [15].…”

“…We have previously reported azaindole derivatives [ 125 I]IPPI [14] and [ 124 I]IPPI [15] as radioiodinated analogs of [ 18 [ 124/125 I]IPPI to Tau was observed in the anterior cingulate of postmortem human AD brains. The binding of [ 124/125 I]IPPI was quantitatively correlated with the Tau load measured by anti-Tau immunohistochemistry of the same subjects [15]. Off-target binding of [ 124/125 I]IPPI to MAO-A or MAO-B would not be a concern because of a lack of effect of clorgyline (MAO-A) or deprenyl (MAO-B) on [ 125 I]IPPI binding in the AD brains [14].…”

“…Off-target binding to MAO-B of these radioiodinated derivatives has not been reported. We have previously reported azaindole derivatives [ 125 I]IPPI [14] and [ 124 I]IPPI [15] as radioiodinated analogs of [ 18 F]MK-6240 for Tau imaging. Selective binding of [ 124/125 I]IPPI to Tau was observed in the anterior cingulate of postmortem human AD brains.…”

“…These attributes can Our previous work with [ 124/125 I]IPPI confirmed the delineation of Tau in the human AD postmortem brain, and they appear to be sensitive to different levels of Tau. They may suggest their ability to differentiate the stage of the disease [14,15]. For in vivo preclinical evaluation, transgenic AD mice models play an essential role in evaluating proteinopathy imaging agents.…”